CO2 reforming of methane was performed on Pt/ZrO2 and Pt/Ce-ZrO2 catalysts at 1073 K under different reactions conditions: (i) atmospheric pressure and CH4 : CO2 ratio of 1 : 1 and 2 : 1; (ii) in the presence of water and CH4 : CO2 ratio of 2 : 1; (iii) under pressure (105 and 190 psig) and CH4 : CO2 ratio of 2 : 1. The Pt supported on ceria-promoted ZrO2 catalyst was more stable than the Pt/ZrO2 catalyst under all reaction conditions. We ascribe this higher stability to the higher density of oxygen vacancies on the promoted support, which favors the cleaning mechanism of the metal particle. The increase of either the CH4 : CO2 ratio or total pressure causes a decrease in activity for both catalysts, because under either case the rate of methane decomposition becomes higher than the rate of oxygen transfer. The Pt/Ce-ZrO2 catalyst was always more stable than the Pt/ZrO2 catalyst, demonstrating the important role of the support on this reaction.